1. Field of the Invention
This invention generally relates to devices for purification and treatment of bodies of water. More particularly, the invention relates to weighted, flexible tubing which is submerged in a body of water for aeration of the water with small bubbles. Special application is found for this approach in natural bodies of water or in wastewater lagoons which are difficult or impractical to drain.
2. Description of Related Art
Aeration of a body of water is beneficial for a number of reasons. For example, it promotes the growth and survival of aerobic micro-organisms, intermediate life forms such as worms and snails, as well as fish and other aquatic wildlife and prevents ice from forming on docks and ships. Perhaps most importantly, aeration is an excellent way to naturally treat wastewater without the introduction of chemicals or the need to remove, haul, and dispose of sludge. In nature, the rolling motion of a river transports oxygen from the water surface to the bottom, which supports riverbed scavengers that digest organic waste and clean the water by converting sludge into carbon dioxide and water. Aeration systems recreate this natural process by providing tubing near the bottom of a body of water and supplying air flow through the tubing. Air slits or orifices in the wall of the tubing or outlet fixtures associated with the tubing allow bubbles to escape into the water, thereby causing the surrounding water to move and circulate in a manner similar to the aforementioned natural rolling motion.
Modern aerators maximize efficiency and performance by providing small bubbles, typically having diameters less than ⅛th of an inch (3.175 mm). This is much preferred to using larger bubbles, because larger bubbles rise quickly through the water, decreasing the contact time between air and water, and create turbulent flow, which can lift sediment off of the bottom surface and disperse it throughout the water. In contrast, smaller bubbles rise slowly and create laminar flow, which increases the residence time of the bubbles in the water without stirring up sediment.
Of course, residence time is increased by situating the aerators at the bottom of the water, but care must be taken to properly orient the aerators during installation. Optimal bubble generation is created when the bubbles are released from the uppermost part of the tubing. If the bubbles are instead released from a lower portion of the tubing, then it is possible that they will merge to form larger bubbles, thereby degrading the performance of the aerator. One approach to properly aligning the tubing is to provide fixtures for immobilizing the tubing, such as the system of U.S. Pat. No. 6,511,054, which is hereby incorporated herein by reference. Another approach has been to provide rigid tubing that will not move or rotate after it has been installed. A typical aerator having such a construction can be seen in U.S. Pat. No. 5,714,062, which is hereby incorporated herein by reference.
While these two approaches are effective in properly orienting the tubing, their usefulness is limited for a number of reasons. Aerators using securing fixtures are generally limited to artificial bodies of water having substantially flat bottoms, in order for the tubing to be properly oriented. Also, it is very difficult to service aerators that are affixed to the bottom of the body of water. As for aerators having rigid tubing, they are relatively expensive and, if they are not secured to the bottom of the body of water, then substantial efforts must be taken to ensure that they are submerged at the proper orientation and remain so oriented.
An alternative approach is to provide tubing that orients itself after being submerged. Such an aerator is shown in U.S. Pat. No. 3,293,861, which is hereby incorporated herein by reference. Such an aerator typically includes flexible tubing with a series of micro-slits and a ballast wire diametrically opposing each other along a length of the tubing. The ballast wire causes the tubing to remain submerged, even when filled with air, and automatically places the micro-slits at the uppermost part of the submerged length of tubing.
Such weighted flexible tubing is preferable to the previously described systems, because it is capable of transferring more oxygen per hp-hour and pumping more gallons of water per hp-hour for many aeration operations, such as deep water installations. However, flexible tubing according to the prior art is difficult and expensive to manufacture and often results in a great deal of wasted wire material. Known flexible tubing includes that manufactured according to a multi-stage process, whereby a thin-walled tube is first extruded to define an air passageway. The thin wall makes it difficult to achieve and maintain during manufacture, installation and use, an air passageway with a truly circular cross-section, and any resulting tube that is not substantially tubular or has an overly thin or thick wall can be rejected as defective or perform with reduced efficiency. When the air passageway has been successfully formed, the tube is passed through the extruder a second time, with a ballast wire pressed thereagainst. By this approach, the tube and ballast wire are joined together by the extruder with a film or skin (typically comprised of the same material as the tube) surrounding their outer surfaces.
After the tubing of this type is thus formed, it typically would be sent to another facility or production line to add micro-slits to the air passageway. The wire keel protrusion makes it difficult to properly align the tubing, which can lead to irregularly spaced, sized, and positioned slits. Furthermore, tubing using a lead ballast wire is even more problematic due to the known harm that lead can cause to the environment and those who handle it. In fact, lead-weighted tubing is prohibited by the U.S. Environmental Protection Agency for use in treating bodies of potable water, even if the lead is fully encapsulated by a non-toxic layer.
Another problem with prior art flexible tubing systems is that they generally have a wall thickness no greater than 0.10-0.20 inch (2.54 mm-5.08 mm). Most often, same is in the range of 0.055-0.075 inch (1.397 mm-1.905 mm). This results in nominal orifice pressure drop, causing uneven air distribution and difficulty controlling bubble size. Also, it is difficult to adequately clean such tubing systems, because a cleaning solution injected into the tubing will be released through the initial slits, while little or no solution remains in the tubing to reach and clean the slits at a far end of the tubing. Finally, thin-walled tubing systems are especially prone to kinking, puncturing, collapsing, tearing, cracking, and other performance-inhibiting maladies caused by transport, installation, temperature extremes, high pressure at great submersion depths, abuse by animals, long-term use, and the like.
Yet another possible drawback of using known thin-wall flexible tubing is lifting it from a body of water for inspection or servicing. Known flexible tubing that has become buried in sludge, mud, gravel or debris—for example, as little as 1-3 inches (2.54 cm-7.62 cm) of sludge coverage—is likely to kink, fold, or break when removed by known means and methods, such as a “J” hook or clamping fixture of a boat. Such damage to the tubing degrades the performance of the air-cuts, even if manufactured to provide preferred bubble formation, with a negative result of having the system “boil” air. When this occurs, the treatment suffers and the tubing needs replacing.
Accordingly, a general object or aspect of the present invention is to provide an improved flexible tubing system for fine bubble aeration.
Another object or aspect of this invention is to provide flexible tubing that is self-submerging and self-aligning without the use of a ballast wire.
Another object or aspect of this invention is to provide flexible tubing with improved durability.
Another object or aspect of this invention is to provide an improved method of manufacturing a flexible tube for fine bubble aeration, typically maintaining oil-less fine bubble release in the top area of the tubing as it rests on or near the bottom of a body of water when in use.
Another object or aspect of this invention is to provide a method for coiling and/or storing a flexible tube for fine bubble aeration.
Another object or aspect is to reduce costs for running aeration systems to treat water and wastewater, preferably without using toxic materials such as lead, including during manufacture, installation or long-term use in water systems.
Other aspects, objects and advantages of the present invention, including the various features used in various combinations, will be understood from the following description according to preferred embodiments of the present invention, taken in conjunction with the drawings in which certain specific features are shown.